Regardless, unless you haven't already I'd suggest trying my ideas, as I did see your video on Discord (just was on the road at the time and forgot to get back on it), and it looked exactly like the problem I had. If you open the AI grid and make it visible to you can see where it's rendered, if the grid dips just straight down on that location to a flat surface way below the actual terrain, then that's another sign it's the same problem I ran into. Some of the terrain worked while other parts didn't, so my guess at the time, and still is, is that the terrain had some borked patches.